Electron accelerator having direct current starting circuit



Nov. 7, 1950 w. F. WESTENDORP ELECTRON ACCELERATOR HAVING DIRECT CURRENT STARTING CIRCUIT 2 Sheets-Sheet 1 Filed May 22, 1947 I Inventor. Wil 1 9m FWesbendorp, 7

Hls Attorney.

WATTLCSS COMPONENT Nov. 7, 1950 Filed May 22, 1947 W. F. WESTEN DORP ELECTRON ACCELERATOR HAVING DIRECT CURRENT STARTING CIRCUIT 2 Sheets-Sheet 2 CA PA Cl TOR CURRENT MA GNET CURRENT VOLTA GE Willem FTWesbendovp, y W 6'. Hi5 Attorngy.

Patented Nov. 7, 1950 ELECTRON ACCELERATOR HAVING DIRECT CURRENT STARTING CIRCUIT Willem F. Westendorp, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application May 22, 1947, Serial No. 749,853

5 Claims. 1

The present invention relates to apparatus for accelerating charged particles and in particular, comprises a magnetic means which is arranged to tune an accelerating circuit which is resonant under normal operating conditions and is nonresonant under starting conditions.

An apparatus whereby charged particles are accelerated by a time-varying magnetic flux is commonly known as a Betatron. A. betatron and its operation are described in Journal of Applied Physics, volume 16 (1945), pages 581 to 593. An apparatus whereby charged particles are accelerated successively by an electric field, and known as a Synchrotron, is described by E. M. McMillan in the Physical Review, volume 68, page 143.

A prior application, Serial No. 639,462, filed January 5, 1946 by Herbert C. Pollock and Willem Westendorp, now matured into United States Patent 2,485,409, which is assigned to the same assignee as the present application, describes apparatus whereby charged particles are caused to be accelerated in an orbital path by cyclically varying magnetic and electric forces operating in succession. The initial acceleration of the charged particles is caused by a time-varying magnetic flux. When the charged particles have been accelerated to a predetermined velocity by the magnetic flu'x, they are additionally accel rated by a cyclic electric field which acts upon the gyrating particles at selected portions of their orbital path.

The present invention is applicable both to apparatus in which the acceleration of charged particles ma be carried out wholly by a magnetic field, as described, for example, in my prior U. S. Patent 2,894,071, atented February 5, 1946, and to apparatus such as is described in the above-mentioned Pollock and Westendorp patent in which magnetic and electric fields successively function to cause acceleration. I-Iowever, it is especially applicable to the latter form of apparatus.

In a batatron such as described in my aforementioned patent, the magneticaccelerating flux is generated in a magnetic core which is provided with one or more windings, arranged to be energized by alternating current. In circuit with such winding or windings is provided sufficient electric capacity to result in resonance at the operating frequency of the apparatus.

However, apparatus providing for acceleration of electrons by a synchronous electric field subsequent to their acceleration by a varying magnetic flux provided with a smaller central core member which saturates early in the cycle of the magnetic field and remains saturated until the magnetic field returns 'to a value near zero, /120 of a second later in the case of 60 cycle operation. When the accelerator is started, the: inductance and capacity of a tunable circuit containing the magnet windings are so far from resonance that excessive current would be drawn from the power lines if it were attempted to start the apparatus at normal operating frequency. No voltage will build up unless line currents many times greater than needed for full voltage steady state operation can be furnished.

In accordance with one aspect of my present invention this difiiculty is overcome by providing the magnetic core of such magnet with magnetizing means energized by direct current whereby the oscillating circuit may be effectively tuned to produce a condition of resonance. In accordance with another aspect of m invention, automatic means is provided for tuning the accelerating winding in response to the phase angle of the input circuit.

In the accompanying drawing, Fig. 1 is a side elevation, partly in section, of an accelerator which is provided with flux regulating windings in accordance with my invention; Fig. 2 is a diagram of an operating circuit; Fig. 3 is a top view of an accelerator shown partly in section; and Figs. 4 and 5 are graphs of current voltage relations.

In Fig. l is shown a sealed rotationally symmetric container !D, which provides an annular path for the acceleration of the charged particles. Ordinarily, it consists of glass. Electrons are provided by an electron gun II, the energizing conductors E2 of which are sealed into a side arm l3. As my present invention is not concerned with the construction of the electron gun and as the electron gun is described in prior patents and other publications, it will not be herein described. The container 5B is highly evacuated and as shown in Fig. 3, is provided on its interior surface with electrodes constituted by coatings l4, [5 of silver, or other suitable conductive material. The function of the electrodes M, 5, separated by gaps !6, ii and being provided with longitudinal subdivisions adjacent the gaps, will be explained hereinafter.

Energizing alternating current is supplied by the windings I8, I13 which function as transformer primaries with respect to the secondary windings 28, 2| on the pole pieces 22, 22' of a shell-type magnetic core 23.

As well understood, the energizing current may be applied directly to the windings 20, 2|, the primary windings l8, [9 being omitted.

When the apparatus is started, and before the central core member 24 is magnetically saturated, the windings 20, 2| and the capacitors 25, 25 (Fig. 2) resonate at a frequency differing from the normal operating frequency. As has been indicated, theapparatus hence will draw an excessive starting current from the supply source, as is shown by the graphs of Figs. 4 and 5. The wattless component of the capacitor current, graph 26, will vary with the voltage at a different rate than the wattless component of the inductive part of the load, graph 21. The latter graph shows the wattless component at different Voltages of the combined wattless ampere turns of coils l8, i9, 20, 2! divided by the number of turns of coils 20 plus 2!. The resultant wattless current in the input circuit 37 which would be obtained at different voltages is indicated by the graph 28 of Fig. 5. The preponderance of capacity in the system initially would cause a large leading wattless current to flow. As the core saturates with rising applied voltage, the wattless component would become lagging as indicated by the graph 28 passing through zero. The actual power loss current or watt component, is too small to be indicated on the scale of Fig. 5.

In accordance with my present invention, the difficulty encountered during starting conditions is overcome by providing automatic means for varying the inductance of the magnetizing circuit. As best shown in Fig. 1, windings 30, 3! are provided on the outer legs 32, 33 of the core 23. The windings 30, 3! are energized with unidirectional current causing saturation of the yokes and legs of the core 23. The flux produced by the direct current excitation passes through the outer members of the core 23 and does not pass through the central portion 22, 22, and 24.

In other words, the inductance of the windings 2! 2| is reduced by the direct current magnetization of the part of the magnetic circuit of these windings which is constituted by the outer members of the core 23. The value of the inductance in the oscillating circuit (constituted by these magnetizing windings and the capacitors) thus can be adjusted to the resonance condition.

' The windings 36, 3| are connected to a source of direct current by the conductors 34, 35 and in series with one another by a conductor 34. Alternating current voltages which are induced in the windings 30, 3| neutralize one another because of their bucking connection and do not appear across the direct current conductors. By an automatic device, which will be described in connection with Fig. 2, the direct current excitation is reduced as the excitation of the magnetization of the core 22 builds up until finally when the alternating current excitation is normal, no direct current remains in the windings 3t, 3!.

In the diagram of electrical connections, shown by Fig. 2, alternating current excitation is supplied by an alternating current source (not shown) through an input circuit 31, in series with a voltage regulator 38 to the primary windings I8, H! which are inductively related to the secondary windings 29, 2!. The latter are connected in series with one another and in series with a capacitor bank represented by capacitors The windings 30, 3! are connected to a source of direct current represented by a threewire system in series with the regulable ohmic resistance 36 and a fixed series resistance 39. Although capable of being adjusted, as shown, the resistance 33 ordinarily is not varied during normal operation. A regulable resistor switch blade 46 is geared to the shaft 4| of the rotor 42 of a direct current motor. The field winding 43 of this motor is connected to the conductor 44 and to the grounded conductor 45 of the three-wire direct current supply system. The conductor 44 of this supply system is connected by a conductor 46, in series with a limit switch 41 to a stationary contact 48. I A second stationary contact 49 is connected by a conductor 50 in series with a limit switch 5! to the direct current conductor 52.

When the apparatus is deenergized, a movable switch blade 53 is caused by the weight 54 to make contact with the contact 49 causing the motor rotor to move the shaft El and the blade 40 to the right, thereby reducing the resistance of the circuit. When the apparatus is started maximum exciting direct current thus is supplied to the windings 30, 3|. By the direct current excitation of windings 3i 3! a desired condition of resonance is established in the circuit containing the alternating current windings 2B and 2 l, and a minimal value of current flows in windings l8 and I9. As the exciting alternating voltage is increased by the voltage regulator 38, the excitation of the stationary selsyn member 55 is increased. It i energized by a transformer 56, the primary winding of which is connected across the circuit 3'5. The movable member 51 of the selsyn is connected by slip rings 58 to a current transformer 59 which is energized from the circuit 3?, as indicated. As excitation builds up in the magnet 22 and the circuit of the windings 20, 2B approximates a state of resonance the movable member of the selsyn device first opens the contact 69 and thereupon causes the switch arm 53 to close the contact 48.

This change in connections energizes the armature to rotate in a reverse direction and insert resistance into the direct current excitation circuit 34, 35 of the windings 3H, 3! and to finally open that circuit. The excitation of these wind ings is decreased and eventually these windings are deenergized when the arm 40 leaves the resistor 35 whereupon the limit switch 41 stops further motion.

By the described operation the regulator for the resistor 36 maintains approximately unity power factor input during the starting period. During normal operation, the magnetizingcircuit operates at resonance and hence the input power factor will be approximately unity.

Although the present invention is not concerned with the operating circuits, such circuits also are indicated conventionally in Fig. 2. As described in my prior Patent 2,394,071, a magnetic peaking strip BI changes cyclically and abruptly from a saturated to an unsaturated condition in accordance with the variation of magnetic field and thereby controls the injection of electrons. When the switch 62 is closed, the variation of voltage across the winding of the peaking strip 58 through the intermediary of a control device 63 energizes a pulse generator 64 which feeds the electron gun ll (Figs. 1 and 3), whereby electrons are introduced into the timevarying magnetic field generated by the windings 2G, 2 i As conventionally indicated in Fig. 2, the electron gun comprises a thermionic filament 65, a focus-sing cup 56 and a housing 5'17. After a predetermined time interval during which the electrons are accelerated solely by a magnetic flux,

a delayed action switching device 68 connects a high frequency source 69 to the electrodes 14, 95 on the interior of the accelerator chamber (see Fig. 2). The high frequency field across the gaps H5, 1'! which operates in synchronisrn with the gyrating electrons imposes additional accelerating forces as the electrons cross these gaps.

After a predetermined period of acceleration, a second electronic delay device 10 effects a discharge of the accelerated electrons for example upon a target 1| (Fig. 1) as well understood;

A copending application, Serial No. 749,852, filed concurrently herewith describes an accelerator for charged particles which is provided with a regulator for varying the effective in,

ductance of a magnetizing circuit and claims broad aspects of such regulator-which include both the present direct current regulating means and also an alternative alternating current regulating means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an accelerator for charged particles comprising a chamber providing an acceleration path for such particles, a magnetic core, means ineluding an oscillation circuit associated with said core for providing a time-varying magnetic ac celeration field, and alternating current input means for supplying energy to said oscillation circuit the improvement which consists in the provision of variable unidirectional magnetizing means on said core and means sensitive to the angular relation of currentand voltage in said input means for controlling said variable unidirectional magnetizing means to vary the magnetization for said core and thereby regulate the resonance condition of said oscillation circuit.

2. In accelerator apparatus of the type which includes a closed container containing a path for the gyration of charged particles, a' magnetic structure outside said container, means for producing therein a time-varying magnetic field, said means including a circuit which is resonant under normal operating conditions of frequency and voltage but is non-resonant under starting conditions, means for tuning said circuit including a plurality ofwindings on said magnetic structure connected in opposition to result in neutralization of variable potentials induced therein during operation and unidirectional energizing core having inductance and capacity proportioned to be in resonant condition during normal operation while said intermediate core member is saturated the improvement which consists in the provision of regulator windings on the outer legs of said core, connections for said windings including a regulable resistance, a power supply circuit for said accelerator, means for energizing said regulator Winding with unidirectional current and means responsive to angular relationof current and voltage in said power circuit for controlling the value of the resistance in said regulator circuit.

4'. An accelerator for charged particles comprising the combination of a shell-type magnetic core, and having pole pieces separated by a gap, an annular acceleration chamber located in said gap, magnetizing windings, a circuit containing capacity connected to said magnetizing windings, an energy input circuit, tuning windings on outer legs of said core, means for energizing said tuning windings with unidirectional current, a resistor for varying the energization of said latter windings, and a regulator for varyingthe effective value of said resistor in response to the phase angle and voltage of said input circuit to maintain approximately unity power factor in- 7 put.

5. An accelerator for charged particles comprising the combination of an evacuated cham her in which charged particles may be accelerated in an annular path, a magnetic core having oppositely located pole pieces Opposite said chamber and having also a saturable central member traversing said chamber, magnetizing windings on said pole pieces, an alternating current supply circuit, an oscillating circuit c0ntaining capacitors connected to said windings,

supplemental windings on said core external to said pole pieces,- a direct current circuit connected to said supplemental windings, a resistor in said circuit, an electric motor for regulating the effective value of said resistance, control means for said motor whereby the motor is caused to vary the effective value of said resistor, and a selsyn device for operating said control means in response to electric conditions of said alternating current supply circuit.

WILLEM F. WESTENDORP;

REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,297,305 Kerat Sept. 29, 1942 2,331,788 Baldwin Oct. 12, 1943 2,394,071 Westendorp Feb. 5, 1946 

